Certain mitogenic hormones and tumor promoters rapidly increase the permeability of quiescent fibroblasts to sodium ions. We are using smooth muscle cells cultured from rat aorta to hormonally modulate sodium transport and examine the effect on cell proliferation. Recently, we reported that angiotensin increases the rate of sodium entry in cultured vascular smooth muscle cells. These findings indicate: (1)\that the effects of angiotensin on sodium transport are probably mediated by high affinity receptors on the cell surface; and (2)\that angiotensin activates a sodium transporter that is selectively inhibited by amiloride. Two ionophores that increase cellular calcium, A23187 and ionomycin, markedly stimulate the rate of amiloride-sensitive sodium uptake in these cells. An intracellular calcium antagonist, 8-(N,N-diethylamino)-octyl3,4,5-trimethoxybenzoate, prevented both the ionophores and angiotensin from stimulating sodium uptake. It is not yet known if calcium entry blockers also prevent the stimulation of sodium transport by angiotensin. Initial observations by us and others suggest that angiotensin may slightly enhance cell multiplication. The effects of angiotensin and other hormones are being tested on DNA synthesis in quiescent cultures of vascular smooth muscle cells. The effect of angiotensin on calcium transport also will be studied.